Nowadays, in order to meet the demand for ever increasing system capability and support a larger amount of communication devices, a system carrier bandwidth of a wireless communication network is growing broader and broader, from 100 MHz to 1 GHz, for example. In practice, not all the communication devices could support a full system carrier bandwidth due to hardware and cost restrictions. A communication device which supports a narrower frequency band could be configured to operate in a sub-band of the system carrier. Furthermore, not all the services require such a large system carrier bandwidth, therefore a communication device which supports a full system carrier bandwidth may also be configured to operate in a sub-band when its service only needs a narrower frequency bandwidth for power saving consideration, for example.
In practice, there may be a plurality of sub-bands for a system carrier in a wireless network, and reference signals for mobility measurement, such as Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS) for Long Term Evolution (LTE) systems for example, are only transmitted over certain sub-bands out of the plurality of sub-bands. For a communication device operating in a sub-band without the reference signals for mobility measurement, since there are no reference signals for mobility measurement in its operation sub-band, a mobility measurement could be a problem for such a communication device.
A measurement gap for mobility measurement may be configured for a communication device, which is operating in a sub-band in which no reference signals for mobility measurement are transmitted. In the configured measurement gap, there is no transmission and reception in the operation sub-band for the communication device, and the communication device measures the signal quality with respect to the reference sequences for mobility measurement and then switches back to the original operation sub-band for continuing data communication, resulting in a negative impact of considerable service interrupt and delay, which may be unacceptable for delay-sensitive services.